Partially coated two-piece tinplate can

ABSTRACT

A two-piece can ( 10 ) having a can body drawn from a tinplate. The can body having an end wall ( 12 ) and an integral side wall ( 14 ) which extends from the periphery of the end wall ( 12 ) to a terminal portion defining a mouth of the body. The can body is provided with a coating ( 24 ) such that the end wall ( 12 ) of the can body being substantially covered with coating ( 24 ) and the side wall ( 14 ) of the can body being substantially an exposed tin surface.

TECHNICAL FIELD

The present invention relates to a two-piece can having at least part of the interior surface formed by exposed tin. The two-piece can is in particular, although not necessarily limited, for the storage of foodstuffs.

BACKGROUND

Many foodstuffs are packaged in cans made from tinplate. The cans may either be three-piece cans or two-piece cans. In three piece cans the cans have a cylindrical side wall including a longitudinal side seam. A can end is attached to one end of the side wall by a double seam to form an open top can. The open top can is filled with product and closed by double seaming a can end to the other end of the side wall. The contents can then be thermally processed in order to be sterilised.

During thermal processing and subsequent storage the product takes up a certain amount of the tin coating in the can thereby preserving the taste and look of the can contents by minimizing oxidation.

In order to reduce the number of seams present the two-piece can was developed where one end of the can and the side wall are formed from a single piece of tinplate in a drawing operation. An example of such an operation is described in European Patent No. 0492870.

Often the foodstuff in the can acts to corrode the layer of tin slowly. In order to reduce this corrosion a coating may be applied to part of the wall of the can. The coating acts to slow down the corrosion of the tin by the can's contents thereby extending the shelf life of the product in the can by increasing the length of time before the contents of the can include the statutory maximum amount of tin.

During the drawing operation to make a two-piece can the side walls are “drawn up” from the end wall of the can and therefore are less thick and include a thinner layer of tin than the end wall of the can. Thus, in order to ensure sufficient tin is available to react to any oxygen in the air to minimise the oxidisation of the foodstuff it is an accepted principle that the tin on the end wall of the can must be exposed to the foodstuff. Therefore, the can body of European Patent No. 0492870 has a lacquered surface forming a region which extends from the part of the wall defining the mouth. The region of the lacquered surface is less than the total length of the side wall and the remaining portion of the side wall and the end wall of the can is an exposed tin zone.

However, this distribution of the tin surface results in the foodstuff present in the upper part of the can being more oxidised than that at the end wall. This two tone effect can diminish the aesthetic appearance of the contents of the can. Additionally, the tin exposure at the end wall can lead to unsightly marks on the end wall of the can.

European Patent No. 2082968 describes another method of lacquering a can made from a tinplate drawing operation which attempts to address these problems. In European Patent No. 2082958 the can body has a plurality of lacquered surface which extend the height of the sidewall and are separated by exposed tin zones. The lacquered surfaces are distributed to limit the aesthetic impact due to chemical action of said foodstuff on said exposed tin zones. However, due to the greatly diminished amount of tin surface available for oxidisation the taste and appearance of the foodstuff in the can will be diminished as it will be exposed to increased oxidisation.

Therefore it is desirable to provide a two-piece can which mitigates one or more of these problems.

SUMMARY

In accordance with the present invention there is provided a can body drawn from a tinplate to comprise an end wall and an integral side wall which extends from the periphery of the end wall to a terminal portion defining a mouth of the body. The end wall of the can body is substantially covered with a coating and the side wall is substantially an exposed tin surface. By applying coating to the inside of the tinplate can in such a manner oxidation of the food contents down the depth of the wall of the can is minimised in a more uniform manner. This means that when the contents of the can are extracted from the can it has a consistent appearance the entire length of the can. Additionally, by applying coating to the end wall of the can the interior of the end wall of the can does not oxidise and therefore no unsightly marks can be seen.

Preferably between 25% and 100% of the end wall is covered with the layer of coating material and even more preferably between 75% and 100% of the end wall is covered with the layer of coating material. The more coating that is applied to the end wall of the can the lower the chances of unsightly marks being formed in the eyeline of a user.

Preferably the coating on the end wall is located centrally and extends radially from the centre of the end wall. This is because when a user looks into a can their eye is drawn to the centre of the can. Therefore by placing the coating in such a position the user is less likely to notice any unsightly marks formed on the inner surface of the end wall of the can by tin oxide.

Optionally the side wall of the can body may be provided with a coating material, the coating material covering between 0% and 50% of the surface area of the side wall. Even more preferably the coating material covers 0 to 20% of the surface area of the side wall. Optionally, the coating material may cover 0 to 10% the surface area of the side wall. The less coating applied to the side wall of the can the greater the amount of tin exposed to the contents of the can thereby minimising the oxidation of the can's contents. Additionally, the less coating applied to the side wall of the can the more uniform the can's contents through the depth of the can.

The side wall may have applied an annular ring of coating adjacent to the terminal portion. This ring prevents unsightly marks on the can's surface caused by any air pockets trapped within the can when it is sealed.

Optionally, at least a portion of the coating on the side wall is deposited in an annular ring located at 50% of the height of the side wall. Alternatively, at least a portion of the layer of coating material is deposited in the part of the side wall adjacent to the end wall.

The side wall of the can may be provided with at least one bead with the side wall being provided with an annular ring of coating over the inner surface of the bead.

The side wall of the can body may be provided with a plurality of beads and an annular ring of coating over the inner surface of at least one of the plurality of beads.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a can according to the invention;

FIG. 2 illustrates a can according to the invention including an annular ring;

FIG. 3 illustrates a can according to the invention including a bead; and

FIG. 4 illustrates a can according to the invention including a bead and an annular ring of coating.

DETAILED DESCRIPTION

A can 10 is made from tinplate by any suitable operation, for example, a drawing operation such as that described in European Patent No. 0492870. The can 10 has an end wall 12 and an integral side wall 14 which has been extended from the end wall 12. The end of the sidewall furthest from the end wall 12 defines an opening 16 through which contents are introduced into the can 10. Once the can has received its contents the opening receives a lid (not shown) which is sealed in place and the can and its contents undergoes the required processing (such as thermal or pressure processing).

The tinplate may be made from a steel matrix having at least the inner surface of its lateral wall provided with a coating of tin and/or tin alloy.

The inner surface of the end wall of the can 10 is provided with a coating 18 forming a layer between the tinplate forming the can and the contents of the can. No coating is provided to the side walls 14 of the can 10. By applying the organic coating to end wall but not to the side walls the tin on the side walls is available to oxidise any oxygen in the can's contents. It has been found that, contrary to previous expectations, the amount of tin present on the side walls of the can sufficiently minimises the oxidisation caused to the contents of the can. This means that there is no region along the length of the can which has a diminished aesthetic appearance due to oxidisation. Additionally, as the end wall of the can does not oxidise due to the coating the formation of unsightly marks on the end wall of the can is inhibited.

When the contents are placed into the can there are often one or more pockets of air trapped at the top of the can between the contents and the lid. In order to mitigate any unsightly marks caused by oxidation of the tin present at the top of the can optionally the can 10 may be provided with a coating 20 at the surface of the side wall of the can 10 proximal to the opening 16 of the can 10 as illustrated in FIG. 2. The coating preferably only extends up to 20% of the height of the side wall. Optionally, the coating may extend only 10% of the height of the side wall.

The side wall of the can may be provided with one or more beads 22 as illustrated in FIG. 3. In such an instance further coating 24 may be provided in an annular ring covering one or more of the beads as illustrated in FIG. 4. This may be in addition to or rather than any coating at the end of the can proximal to the opening.

Optionally, the entire end wall of the can may not be covered with a coating. Rather, between 25% to 100% of the end wall of the can may be coated the coating extending radially from the centre of the end wall. Preferably, more than 75% of the end wall of the can is coated. In alternative embodiments the end wall of the can is provided with one or more beads. In such an instance at least the flat portion of the end wall is provided with a coating.

The coating may be formed of any suitable material. For example it may be chosen from a group comprising epoxy phenolic lacquer, epoxy amine lacquer, acrylic resin lacquer, epoxy polyester lacquer, and vinyl lacquer with or without a pigment.

Although the coating has been described as being applied to the side walls in an annular ring the skilled person will understand that the coating may be applied to the side wall using any desired pattern. For example, it may be provided in irregular areas or in vertical stripes.

The coating may be applied to the surface of the open top can using any suitable method. For example, the coating may be sprayed onto the inner surface of the can using a nozzle. 

1. A can body drawn from a tinplate to comprise an end wall and an integral side wall, the side wall extending from the periphery of the end wall to a terminal portion defining a mouth of the body, wherein at least 25% of the end wall interior surface area is covered with a coating and more than 50% of the side wall interior surface area comprises an exposed tinplate surface.
 2. A can body as claimed in claim 1 wherein between 75% and 100% of the end wall interior surface area is covered with a coating.
 3. A can body as claimed in claim 1 wherein the coating on the end wall is located centrally and extends radially from the centre of the end wall.
 4. A can body as claimed in claim 1 wherein the side wall is provided with a coating material, the coating material covering 0 to 20% of the interior surface area of the side wall.
 5. A can body as claimed in claim 4 wherein the side wall coating forms is applied with an annular ring of coating adjacent to the terminal portion.
 6. A can body as claimed in claim 4 wherein at least a portion of the coating on the side wall is deposited in an annular ring located at 50% of the height of the side wall.
 7. A can body as claimed in claim 4 wherein at least a portion of the coating material is deposited in the part of the side wall adjacent to the end wall.
 8. A can body as claimed in claim 1 wherein the side wall is provided with at least one bead and the interior surface of the side wall is provided with an annular ring of coating over the inner surface of the bead.
 9. A can body as claimed in claim 1 wherein the side wall is provided with a plurality of beads and the interior surface of the side wall is provided with an annular ring of coating over the inner surface of at least one of the plurality of beads.
 10. (canceled) 